CONTRAST-MEDIA AS EXTRACELLULAR FLUID SPACE MARKERS - ADAPTATION OF THE CENTRAL VOLUME THEOREM

We present some theoretical observations on the pharmacokinetics of th e conventional intravascular radiographic and gadolinium chelate MR co ntrast agents. These agents may be viewed from a physiological perspec tive as extracellular fluid (ECF) space markers. It can be shown that the passage of such agents through the body may be described by a vari ant of the ''central volume theorem'', if the central volume is taken to be that of the entire extracellular fluid. A consequence is that, i n a manner akin to nuclear medicine techniques utilizing technetium-99 m diethylene triamine pentacetic acid (DTPA), measures of glomerular f iltration rate (GFR) related to total ECF volume rather than to the no rmal body surface area may be obtained from direct or indirect measure ments of iodine or gadolinium plasma levels. Typical measurements are presented. A simple means is also described of generating curves of th e fraction of contrast medium excreted from the body, applicable to bo th patients with normal and with abnormal renal function.